1. Field of the Invention
This invention relates to a multi-gear changing mechanism for use with various kinds of bicycle pedals. It is, in specific terms, a 3-speed free wheel operated by forward or backward pedalling.
2. Description of the Prior Art
The ordinary free wheel on a bicycle pedal is for effecting motion only. To achieve gear change there must be a mechanism, which is in most cases composed of a set of coaxial sprocket wheels or a free wheel combined with sprocket wheels. It's a complicated device of relatively high cost and requires the user exercise care while shifting gears. A little negligence might damage the chain or gear teeth. Besides, its transmission power is low and wears out soon.
Previously, the inventor of this invention had designed a two-way-driven 2-speed free wheel (New utility model patent NO. 8520575, Chinese Patent Office) which is capable of gear-changing as well as motion transmission. It is composed of a sprocket wheel, a central gear, catches, cones, etc. It is characterized in that the sprocket wheel has sprockets on the outer edge and gear teeth on the inner edge. Between the sprocket wheel and central gear there are two or more planet pinions fixed on a planet pinion bearing collar and engaging with the central gear and the inner teeth of the sprocket wheel. A catch, hinged on the bottom forks of a bicycle (hereafter referred to as an outer catch), has its tapered end fitted into the ratchet teeth on the side of the planet pinion bearing collar or into outer ratchet teeth on an outer ring. There are also two or more self-locking catches built in the free wheel with their tapered ends fitting into the inner teeth of the sprocket wheel (hereafter referred to as inner catches).
When the sprocket wheel rotates clockwise (in forward direction), the free wheel is in low gear, and when it rotates counterclockwise the free wheel is in high gear. When the sprocket wheel of the free wheel rotates counterclockwise, it will have the inner catches move with the same speed and in the same direction as it. As these catches are fixed on the planet pinion bearing collars, it will rotate, together with the planet pinions attached to it, with the same speed and in the same direction as the sprocket wheel. And the central gear, driven by the planet pinions, will also rotate with the same speed and in the same direction as the sprocket wheel. As this free wheel has a bigger circumference than an ordinary free wheel, the bicycle installed with such a free wheel has, under such condition, a lower speed than one installed with an ordinary free wheel, if their chain wheels rotate with the same speed.
If the chain wheel is back-pedalled, the sprocket wheel of the free wheel will rotate in the same direction and the inner catches will not be interlocked with the planet pinions and the planet pinion bearings. In this case, the planet pinions, engaged with the inner teeth of the sprocket wheel, as well as the planet pinion bearings, are being pushed to rotate with it in a backward direction. But the planet pinion bearing collar is stopped by the catch hinged on the bottom forks, so the planet pinions can only turn to drive the central gear in a forward direction. Thus, the back-pedalling of the chain wheel causes the bicycle to go forward as usual, but in a higher speed.
That device has a variation model, one-way-drive 2-speed free wheel. Its structure is a little different. The sprocket wheel has no inner teeth, while an outer ring has. Each of them can rotate independently of the other. The outer ring has outer ratchet teeth on its outer edge, to be locked by the outer catch. And the sprocket wheel is fastened with the planet bearing collar by a screw thread fitting.
When the outer ring is locked by the outer catch, the forward rotation of the sprocket wheel is to drive the planet pinion bearing collar to rotate in a forward direction. But since the outer ring is locked, the planet pinions can only rotate in a backward direction and drive the central gear to rotate in a forward direction. Under such condition the bicycle runs in high gear.
If the outer catch is disengaged from the ratchet teeth on the outer ring, the planet pinion bearing is to rotate in a forward direction with the forward rotation of the sprocket wheel and cause the outer ring to rotate in a backward direction. But since the inner teeth of the outer ring are locked with the inner catches, the planet pinions keep from turning. Under such condition the central gear rotates with the sprocket wheel at the same speed and the bicycle runs in low gear.
Both of the above-mentioned structures are simpler than the prevailing built-in gear-changing mechanism or the outer one. Compact in form, they are secure and withstand wear and tear. Each can easily be installed on an ordinary pedal cycle. Besides, each can be installed on a fitness bike.
The only shortcoming is the inner catches, which are susceptible to damage under great stress when they are locked.